Numerous ophthalmic surgical procedures, such as for correcting myopia or hyperopia, require one or more steps of resectioning the cornea of the eye. A variety of devices called keratomes have been developed over recent decades to perform such corneal resectioning. Referring to FIGS. 1, 2a and 2b, a typical resectioning operation will separate flap 6 of corneal tissue 2 from eyeball 4. The tougher outer layers of epithelial cells 8 are separated and lifted away to expose the more compliant inner layers 12 of cornea 2, but the separated outer layers are left attached as flap 6. Once exposed, interior layers 12 of cornea 2 will to some extent adjust themselves, or their shape may be altered through further surgical steps. Such further steps may include, for example, making radial keratotomy cuts or performing a subsequent resectioning which may include removing a contoured layer of corneal tissue. At the conclusion of the various steps of the surgical procedure, flap 6 is typically replaced over inner corneal tissues 12 to protect the healing tissues.
The representative keratomes described in U.S. Pat. Nos. 5,496,339 issued to Koepnick, and Re. 35,421 issued to Ruiz et al., which are depicted in FIGS. 3a and 3b, demonstrate many standard features of prior art keratomes. A retaining ring for positioning and retaining the subject eyeball is typically supplied with a source of vacuum. The vacuum pressure draws the eyeball into the retaining ring so that the cornea protrudes through the retaining ring and presses against the surface of a feature, herein referred to as an applanation shoe, which is provided to restrain the protruding cornea. The applanation shoe is desirably made of transparent material to help the surgeon to position the cornea and to observe it during the surgery. A cutting blade is then drawn across the positioned cornea to a preset stopping point, desirably oscillating as it is moved forward. Both the thickness and the expanse of the corneal tissue which is cut must be carefully controlled. The separated portion of the cornea may be completely removed, but typically one edge of the sectioned layer is left attached to form flap 6 which can easily be replaced over the cornea after the surgery.
Keratomes must have a mechanism by which the knife blade is guided. Proximate to the cutting location, the prior art keratomes all have blades rubbing on guides, or metal rubbing on metal, such as drive gears. Unfortunately, such rubbing can result in shavings being created and entering the surgical site. Referring to FIG. 3a, the keratome of Ruiz et al. has an intricate mechanism with metal-on-metal gears rubbing in the surgical vicinity. For example, pinion 834 rides on track 891 which is part of positioning ring 890; and endless pinion 822, along with its eccentric shaft and associated pinions, operates directly above the blade cutting site (not shown). In FIG. 3b, the keratome of Koepnick is seen to have blade 954 which rubs directly on the insert 948 and slides in surfaces defined along line 991. The sliding surfaces at 991 are located directly above positioning suction ring 990, and the rubbing surface between blade 954 and insert 948 is directly adjacent regions of intimate contact between the corneal tissue and insert 948. Thus, these two prior art keratome examples have rubbing between the cutting blade and other surfaces, and rubbing of gears, very close to the surgical site.
Another drawback of existing keratomes is the inconvenience of maintaining surgical cleanliness. Since parts of the keratome must be in intimate contact with tissues around and including the surgical site, it is necessary to ensure a high degree of cleanliness and sterility. The relatively intricate mechanisms which prior art keratomes position near the surgical site, as described above, have not been well-adapted for ease of cleaning and autoclaving.
Thus, a need exists for an easily used keratome able to perform precise resectioning operations, while facilitating surgical cleanliness by avoiding creation of shavings which might contaminate the surgical site, and by being easily cleaned, sterilized, and replaced.